The present invention is directed towards an improved cooling system for a gas turbine. More particularly, the present invention is directed towards an improved cooling system which utilizes a cylindrical distribution channel having a plurality of V-shaped notch weirs formed therein for metering coolant into a plurality of platform and airfoil distribution channels located in the buckets of the gas turbine.
The cooling system of the present invention is utilized in connection with a gas turbine of the type including a turbine disk mounted on a shaft rotatably supported in a casing and a plurality of turbine buckets extending radially outward from the disk. Each of the buckets includes a root portion mounted in the disk, a shank portion extending radially outward from the root portion to a platform portion, and an airfoil extending radially outward from the platform portion. During operation, the buckets receive a driving force from hot fluid moving in a direction generally parallel to the axis of the shaft and convert this driving force to rotational motion which is transmitted to the shaft via the turbine disk. As the result of the relatively high temperatures of the hot fluid, a significant amount of heat is transferred to the turbine buckets. In order to remove this heat from the bucket structure, the prior art has developed a large variety of open-liquid cooling systems. Exemplary of such systems are U.S. Pat. No. 3,658,439, issued to Kydd; U.S. Pat. No. 3,804,551, issued to Moore; U.S. Pat. No. 4,017,210, issued to Darrow; and U.S. application Ser. No. 910,500, filed May 30, 1978 now U.S. Pat. No. 4,212,587 in the name of Michael Horner. The disclosures of the foregoing patents are incorporated herein by reference.
Open circuit liquid cooling systems are particularly important because they make it feasible to increase the turbine inlet temperature to an operating range of from 2500.degree. F. to at least 3500.degree. F. thereby obtaining an increase in power output ranging from about 100-200% and an increase in thermal efficiency ranging to as high as 50%. A primary requirement of open circuit liquid cooling systems is that the liquid coolant be evenly distributed to the several platform and airfoil distribution channels formed in the bucket. Such a distribution is difficult to obtain as a result of the extremely high buckets tip speeds employed, resulting in centrifugal fields of the order of 25,000 G. To obtain an even flow of coolant liquid throughout the several coolant channels, the prior art systems, as exemplified by U.S. Pat. Nos. 3,804,551 and 4,017,210, utilize weir structures which meter the amount of coolant liquid supplied to each individual channel from pools of coolant liquid formed in the platform portion of the bucket. Particularly, these systems introduced liquid coolant into each end of a trough formed in the platform portion of the bucket such that liquid coolant flows in a direction parallel to the axis of rotation of the turbine disk from each end of the trough. The liquid coolant flows over the top of an elongated weir which performs the metering for each channel. In order to perform satisfactorily, it is critical that the top of the prior art weir is parallel to the axis of rotation of the turbine within a tolerance of several mils. If this relationship is not maintained, all of the coolant liquid will flow over the low end of the weir and consequently, some of the coolant channels formed in the platform and airfoil of the bucket will be starved for coolant.